Method for producing cationic surface sizing agent, and sizing agent obtained by method

ABSTRACT

The present invention relates to a method for producing a cationic surface sizing agent, and contains a first step of obtaining a copolymer (A) by solution-polymerizing a monomer mixture containing a monomer having a tertiary amino group (a), a specific (meth)acrylic acid ester (b) and styrenes (c) in the specific proportion in the presence of a chain transfer agent; a second step of obtaining a copolymer (B) by polymerizing the copolymer (A) and a hydrophobic monomer (d), in order to have a specific proportion of the copolymer (A), in an oxidation-reduction system using a water-soluble free-radical initiator and a heavy metal salt in the absence of a surfactant; and a third step of obtaining a quaternary ammonium salt of the copolymer (B) by quaternizing a tertiary amino group present in the copolymer (B).

TECHNICAL FIELD

The present invention relates to a method for producing a cationicsurface sizing agent, a sizing agent obtained by the method, and paperand a paper board coated with the sizing agent.

BACKGROUND ART

Conventional cationic surface sizing agents usually contain styrenes anda monomer having a tertiary amino group (i.e., a cationic monomer) as amain component. The sizing agent is an aqueous solution of a copolymerhaving a tertiary amino group obtained by polymerizing the monomercomponent, or a copolymer having a quaternary ammonium salt groupobtained by quaternizing the tertiary amino group (Patent Documents 1and 2). These copolymers are prepared by the following method.

(i) Solution-polymerization using an oil-soluble polymerization catalystis performed in an organic solvent or a mixed solvent of an organicsolvent and water.(ii) Emulsion-polymerization using a water-soluble polymerizationcatalyst is performed in a water-based solvent.

The cationic surface sizing agent obtained by such a method has a goodsizing property, but has a problem that it is susceptible to environmentof usage, especially influences of water (hardness, pH, etc.) and itsstability is insufficient.

On the other hand, in the cationic surface sizing agent obtained byperforming emulsion-polymerization in water without using an organicsolvent, or in the cationic surface sizing agent obtained by performingemulsion-polymerization of a cationic polymer obtained bysolution-polymerization and a hydrophobic monomer, a surfactant is oftenused as an emulsifier (Patent Documents 3 to 7). Anemulsion-polymerization product using the surfactant is less susceptibleto an impact of environment of usage than the cationic surface sizingagent obtained by the solution-polymerization, and an improvement instability can be expected, but the improvement effect is not adequate.Furthermore, such emulsion-polymerization product is inferior in theeffect of imparting a sizing property to the cationic surface sizingagent obtained by the solution-polymerization because of use of asurfactant.

Further, a production method in which emulsion-polymerization isperformed without using the surfactant is known (Patent Documents 8 and9). In the cationic surface sizing agent obtained without using thesurfactant, an aqueous solution of a cationic polymer obtained bysolution-polymerization is used as a dispersing agent. Hence, thecationic surface sizing agent exhibits the stability equal to and thesizing property higher than the sizing agent using the surfactant.However, the cationic surface sizing agent obtained by theemulsion-polymerization is inferior in the effect of imparting a sizingproperty to the cationic surface sizing agent obtained by thesolution-polymerization.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2006-161259-   Patent Document 2: Japanese Unexamined Patent Publication No.    2006-322093-   Patent Document 3: Japanese Unexamined Patent Publication No.    11-256496-   Patent Document 4: Japanese Unexamined Patent Publication No.    11-279983-   Patent Document 5: Japanese Unexamined Patent Publication No.    2001-262495-   Patent Document 6: Japanese Unexamined Patent Publication No.    2006-016712-   Patent Document 7: Japanese Unexamined Patent Publication No.    2009-242686-   Patent Document 8: Japanese Unexamined Patent Publication No.    2002-129494-   Patent Document 9: Japanese Unexamined Patent Publication No.    2008-501830

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

It is an object of the present invention to provide a cationic surfacesizing agent which has excellent dispersion stability and imparts anexcellent sizing property regardless of environment of usage, especiallywater conditions (hardness, pH, etc.) or paper types (paper, paperboard, etc.) to which the sizing agent is applied.

Solutions to the Problems

The present inventors made earnest investigations in order to solve theabove-mentioned problem, and consequently completed the followinginvention:

(1) A method for producing a cationic surface sizing agent containing afirst step of obtaining a copolymer (A) by solution-polymerizing amonomer mixture which contains a monomer having a tertiary amino group(a) in the amount of 15 to 45% by weight, a (meth)acrylic acid ester (b)in the amount of 15 to 85% by weight, and styrenes (c) in the amount of0 to 70% by weight in the presence of a chain transfer agent, wherein anester moiety of the (meth)acrylic acid ester (b) is a chainlike alkylhaving 4 to 18 carbon atoms, a cyclic alkyl having 4 to 18 carbon atoms,or aryl having 6 to 18 carbon atoms;

a second step of obtaining a copolymer (B) by polymerizing the copolymer(A) and a hydrophobic monomer (d) in an oxidation-reduction system usinga water-soluble free-radical initiator and a heavy metal salt in theabsence of a surfactant, wherein the copolymer (A) is used at theproportion of 30 to 70% by weight with respect to the entire componentsincluding the copolymer (B), and the monomer having a tertiary aminogroup (a) is used so as to be 8 to 20% by weight with respect to theentire components including the copolymer (B); and

a third step of obtaining a quaternary ammonium salt of the copolymer(B) by quaternizing a tertiary amino group present in the copolymer (B).

(2) The method according to the paragraph (1), wherein the water-solublefree-radical initiator is hydrogen peroxide, and the heavy metal salt isferrous sulfate.

(3) The method according to the paragraph (1) or (2), wherein thetertiary amino group moiety present in the copolymer (A) is completelyneutralized by using acid to be brought into the form of an aqueoussolution in the first step.

(4) The method according to any one of the paragraphs (1) to (3),wherein the copolymer (A) has an average particle diameter of 50 nm orless.

(5) The method according to any one of the paragraphs (1) to (4),wherein the quaternary ammonium salt of the copolymer (B) has an averageparticle diameter of 100 nm or more.

(6) The method according to any one of the paragraphs (1) to (5),wherein 50 mol % or more of the tertiary amino group present in thecopolymer (B) is quaternized.

(7) The method according to any one of the paragraphs (1) to (6),wherein the quaternization is performed by using epichlorohydrin.

(8) The method according to any one of the paragraphs (1) to (7),wherein the monomer having a tertiary amino group (a) is at least oneselected from the group consisting of dialkylaminoalkyl (meth)acrylateand dialkylaminoalkyl (meth)acrylamide.

(9) A cationic surface sizing agent produced by the method according toany one of the paragraphs (1) to (8).

(10) A method for surface treating paper or a paper board, comprising astep of coating the surface of the paper or paper board with thecationic surface sizing agent according to the paragraph (9) or amixture of this sizing agent and a water-soluble high-molecularcompound.

(11) Paper or a paper board prepared by the method according to theparagraph (10).

(12) The paper or paper board according to the paragraph (11), whereinthe paper or paper board before coated with a cationic surface sizingagent is paper or a paper board not including an internal sizing agent,a neutralized paper having a Stockigt sizing degree of 2 second or lessand a pH of paper surface of 6.5 to 8.5, or a neutralized paper boardhaving water absorbency by a two minutes Cobb test of 100 g/m² or moreand a pH of paper surface of 6.5 to 8.5.

Effects of the Invention

In accordance with the present invention, the effect of enabling toprovide a cationic surface sizing agent, which has excellent dispersionstability and imparts an excellent sizing property regardless ofenvironment of usage, especially water conditions (hardness, pH, etc.)or paper types (paper, paper board, etc.) to which the sizing agent isapplied, is achieved.

That is, it is possible to improve the compatibility of the copolymer(A) with the copolymer (B) by undergoing the first step and the secondstep to obtain the copolymer (B). Further, the cationic surface sizingagent becomes less susceptible to the hardness or the pH of water to beused by bringing the copolymer (B) into the form of a quaternaryammonium salt. Further, it is possible to attain a sizing agent havingthe effect that the surface sizing agent is uniformly dispersed withoutbeing agglomerated when it is diluted to a concentration of a coatingsolution. Accordingly, even when paper or a paper board not containingan internal sizing agent, a neutralized paper having a Stockigt sizingdegree of 2 second or less, or a neutralized paper board having waterabsorbency by a two minutes Cobb test of 100 g/m² or more is coated withthe surface sizing agent, the amount of the surface sizing agent, whichis distributed over the surface of paper without being dispersedthroughout the whole paper in the form of agglomerated molecules, isincreased. It is thought that as a result of the above, thehydrophobicity of the surface sizing agent is adequately exerted on thesurface of paper.

EMBODIMENTS OF THE INVENTION

A method for producing a cationic surface sizing agent of the presentinvention contains a first step of obtaining a copolymer (A) bysolution-polymerizing a monomer mixture which contains a monomer havinga tertiary amino group (a) in the amount of 15 to 45% by weight, a(meth)acrylic acid ester (b) in the amount of 15 to 85% by weight, andstyrenes (c) in the amount of 0 to 70% by weight in the presence of achain transfer agent, wherein an ester moiety of the (meth)acrylic acidester (b) is alkyl having 4 to 18 carbon atoms;

a second step of obtaining a copolymer (B) by polymerizing the copolymer(A) and a hydrophobic monomer (d) in an oxidation-reduction system usinga water-soluble free-radical initiator and a heavy metal salt in theabsence of a surfactant, wherein the copolymer (A) is used at theproportion of 30 to 70% by weight with respect to the entire componentsincluding the copolymer (B), and the monomer having a tertiary aminogroup (a) is used so as to be 8 to 20% by weight with respect to theentire components including the copolymer (B); and

a third step of obtaining a quaternary ammonium salt of the copolymer(B) by quaternizing a tertiary amino group present in the copolymer (B).Hereinafter, the present invention will be described in detail.

<Method for Producing Cationic Surface Sizing Agent>

(First Step)

The first step is a step of obtaining a copolymer (A) bysolution-polymerizing a monomer mixture including a monomer having atertiary amino group (a) (hereinafter, sometimes referred to as merely“component a”), a specific (meth)acrylic acid ester (b) (hereinafter,sometimes referred to as merely “component b”) and styrenes (c)(hereinafter, sometimes referred to as merely “component c”) in thespecific ratio in the presence of a chain transfer agent.

The monomer having a tertiary amino group (component a) used in theproduction method of the present invention is not particularly limitedas long as it is a monomer which has a tertiary amino group in amolecule and can be copolymerized with the (meth)acrylic acid ester (b)and the styrenes (c), respectively described later. Examples of suchcomponent a include dialkylaminoalkyl (meth)acrylate, dialkylaminoalkyl(meth)acrylamide and the like.

Examples of dialkylaminoalkyl (meth)acrylate include dimethylaminoethyl(meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminoethyl(meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl(meth)acrylate and the like.

Examples of dialkylaminoalkyl (meth)acrylamide includedimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide,dimethylaminopropyl (meth)acrylamide, diethylaminopropyl(meth)acrylamide and the like.

Among these components a, dimethylaminoethyl (meth)acrylate ordimethylaminopropyl (meth)acrylamide is preferable.

The component a is contained in the monomer mixture forming thecopolymer (A) in the proportion of 15 to 45% by weight. When theproportion of the component a is less than 15% by weight, thehydrophilicity of the copolymer (A) is poor, and the copolymer (A)cannot be uniformly dispersed in water. On the other hand, when theproportion of the component a is more than 45% by weight, thehydrophobicity of the copolymer (A) is poor to cause the sizing propertyof the resulting sizing agent to be poor. The component a is containedpreferably in the proportion of 18 to 40% by weight, and more preferablyin the proportion of 20 to 35% by weight.

The components a may be used singly or may be used in combination of twoor more thereof. When the components a are used in combination of two ormore thereof, the total content of the combination is adapted to satisfythe above range.

The specific (meth)acrylic acid ester (component b) used in theproduction method of the present invention is a (meth)acrylic acidester, an ester moiety of which is a chainlike alkyl having 4 to 18carbon atoms, a cyclic alkyl having 4 to 18 carbon atoms, or aryl having6 to 18 carbon atoms. That is, the specific (meth)acrylic acid ester isa (meth)acrylic acid ester, in which R of CH₂═CH—COOR or CH₂═C(CH₃)—COORis an alkyl group having 4 to 18 carbon atoms, a cyclic alkyl grouphaving 4 to 18 carbon atoms, or an aryl group having 6 to 18 carbonatoms.

Examples of such component b include isobutyl (meth)acrylate, n-butyl(meth)acrylate, ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl(meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate,benzyl (meth)acrylate and the like. Among these, isobutyl(meth)acrylate, n-butyl (meth)acrylate, and ethylhexyl (meth)acrylateare preferable.

The component b is contained in the monomer mixture forming thecopolymer (A) in the proportion of 15 to 85% by weight. When theproportion of the component b is less than 15% by weight, the sizingproperty of the resulting sizing agent is poor. On the other hand, whenthe proportion of the component b is more than 85% by weight, thehydrophilicity of the copolymer (A) is poor, and the copolymer (A)cannot be uniformly dispersed in water. The component b is containedpreferably in the proportion of 20 to 80% by weight, and more preferablyin the proportion of 40 to 80% by weight.

The components b may be used singly or may be used in combination of twoor more thereof. When the components b are used in combination of two ormore thereof, the total content of the combination is adapted to satisfythe above range.

The styrenes (component c) used in the production method of the presentinvention is not particularly limited as long as it is a monomer whichcan be copolymerized with the component a and the component b. Examplesof the component c include styrene, α-methylstyrene, vinyl toluene,ethyl vinyl toluene, chloromethyl styrene and the like. Among these,styrene, α-methylstyrene, and vinyl toluene are preferable.

The component c is contained in the monomer mixture forming thecopolymer (A) in the proportion of 0 to 70% by weight. When theproportion of the component c is more than 70% by weight, the ability ofthe monomer to be copolymerized in a solution-polymerization is poor.When the ability of the monomer to be copolymerized is poor, aneffective component in the surface sizing agent agglomerates to formmicrograins which are scattered on the surface of paper and can onlynon-uniformly cover the paper, and therefore a sizing effect is reduced.The component c is contained preferably in the proportion of 0 to 50% byweight, and more preferably in the proportion of 0 to 40% by weight.

The components c may be used singly or may be used in combination of twoor more thereof. When the components c are used in combination of two ormore thereof, the total content of the combination is adapted to satisfythe above range.

Moreover, the monomer mixture may contain monomers other than thecomponents a, b and c to such an extent that the effect of the presentinvention is not impaired. Examples of such monomers include compoundshaving a vinyl group or an allyl group such as short chain alkyl(meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate,n-propyl (meth)acrylate, isopropyl (meth)acrylate and the like; hydroxylgroup-containing (meth)acrylates such as hydroxypropyl (meth)acrylate,2-hydroxyethyl (meth)acrylate and the like; (meth)acrylamide; andacrylonitrile.

The copolymer (A) is obtained by solution-polymerizing a monomer mixturecontaining the above-mentioned components a, b and c in the presence ofa chain transfer agent. The solution-polymerization of a monomer mixtureis not particularly limited. For example, it is performed by a usualradical polymerization.

A solvent used in solution-polymerization can be appropriately selectedaccording to the composition of the monomer mixture. Examples of thesolvent include isopropyl alcohol, n-butanol, isobutanol, t-butanol,sec-butanol, acetone, methyl ethyl ketone, methyl n-propyl ketone,3-methyl-2-butanol, diethyl ketone, methyl isopropyl ketone, methylisobutyl ketone, diisopropyl ketone, ethyl benzene, toluene and thelike. Among these, isopropyl alcohol, methyl isobutyl ketone, andtoluene are preferably used.

The chain transfer agent is used for controlling a weight averagemolecular weight of the copolymer (A). Examples of the chain transferagent include oil-soluble chain transfer agents (for example, mercaptanssuch as t-dodecylmercaptan, n-dodecyl mercaptan, n-octyl mercaptan,mercaptopropionic acid dodecyl ester and the like, cumene, carbontetrachloride, α-methylstyrene dimer, terpinolene, etc.), andwater-soluble chain transfer agents (for example, mercaptoethanol,thioglycolic acid and salt thereof, etc.). The chain transfer agent canbe appropriately selected according to a solvent or the composition of amonomer mixture. An amount of the chain transfer agent can beappropriately determined so as to obtain the copolymer (A) having adesired weight average molecular weight.

The polymerization initiator is not particularly limited, and examplesthereof include azo-type initiators (e.g., azobismethylbutyronitrile,dimethyl azobis isobutylate, azobisdimethylvaleronitrile,azobisisobutyronitrile, etc.), and peroxide-type polymerizationinitiators (e.g., hydrogen peroxide, benzoyl persulfate, t-butylperoxybenzoate, t-butyl peroxy isopropyl monocarbonate, t-butylperoxy-2-ethyhexanoate, cumene hydroperoxide, etc.). An amount of thepolymerization initiator is not particularly limited, and it can beappropriately determined according to the composition of a monomermixture.

A temperature or a time of the polymerization reaction is notparticularly limited, and it can be appropriately set according to asolvent, the composition of a monomer mixture and a polymerizationinitiator to be used. The polymerization reaction is usually carried outat a temperature of 80 to 120° C., preferably 85 to 115° C. Further, areaction time is usually 2 to 6 hours, and preferably 3 to 5 hours.

The copolymer (A) thus obtained is preferably solubilized in water forsubjecting it to a subsequent step. For example, it is preferred tocompletely neutralize the tertiary amino group moiety present in thecopolymer (A) by using acid such as hydrochloric acid, sulfuric acid oracetic acid to bring the tertiary amino group moiety into the form of anaqueous solution. Moreover, the copolymer (A) preferably has an averageparticle diameter of 50 nm or less, and more preferably an averageparticle diameter of 30 nm or less.

(Second Step)

The second step is a step of obtaining a copolymer (B) by polymerizingthe copolymer (A) and a hydrophobic monomer (d) (hereinafter, sometimesreferred to as merely “component d”) under the specific conditionswithout using a surfactant.

The hydrophobic monomer (component d) used in the production method ofthe present invention is not particularly limited as long as it is amonomer which can be copolymerized with the copolymer (A). Examples ofthe component d include styrene, 2-ethylhexyl (meth)acrylate, methyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl(meth)acrylate and the like.

In the second step, the copolymer (A) is used at the proportion of 30 to70% by weight with respect to the entire components forming thecopolymer (B), and the component a is used so as to be 8 to 20% byweight with respect to the entire components forming the copolymer (B).A good sizing property and dispersibility can be attained by using thecopolymer (A) and the component a to have a specific proportion.

The copolymer (A) is used at the proportion of 40 to 70% by weight withrespect to the entire components forming the copolymer (B), and thecomponent a is used so as to be 8 to 18% by weight with respect to theentire components forming the copolymer (B).

A polymerization reaction of the copolymer (A) with the component d isperformed by using an oxidation-reduction system using a water-solublefree-radical initiator and a heavy metal salt, namely, a redox catalystwithout using a surfactant. When the polymerization reaction of thecopolymer (A) with the component d is performed by using theoxidation-reduction system, namely, the redox catalyst, a homopolymer ofthe component d is hardly synthesized, and a graft copolymer (copolymer(B)) of the copolymer (A) and the component d, which is intended in thepresent invention, becomes easy to be synthesized. Accordingly, a sizingagent having excellent dispersibility and enabling to impart anexcellent sizing property can be obtained. Further, since the surfactantis not used, a polymer, which is composed of only the component ddispersed by the surfactant, is hardly synthesized, and since the sizingagent ultimately obtained does not the surfactant, a further improvementin the effect of imparting a sizing property can be expected.

Examples of the water-soluble free-radical initiator include peroxocompounds, azo compounds, hydrogen peroxide, persulfate and the like,and examples of the heavy metal salt include cerium, manganese, iron(II) and the like. Among these, a combination of hydrogen peroxide andferrous sulfate is preferable.

A reaction temperature and a reaction time of the polymerizationreaction in the second step are not particularly limited, and it can beappropriately set. The polymerization reaction is usually carried out ata temperature of 70 to 90° C., preferably 75 to 90° C. Further, thereaction time is usually 1 to 5 hours, and preferably 2 to 4 hours.

(Third Step)

The third step is a step of obtaining a quaternary ammonium salt of thecopolymer (B) by quaternizing a tertiary amino group present in thecopolymer (B).

The proportion of a tertiary amino group quaternized among the tertiaryamino groups present in the copolymer (B) is not particularly limited.For example, preferably, 50 mol % or more of the tertiary amino group isquaternized, and more preferably, 60 mol % or more of the tertiary aminogroup is quaternized.

The quaternization is usually performed by using a quaternizing agentsuch as epihalohydrin, for example, epichlorohydrin and epibromohydrin.

The quaternary ammonium salt of the copolymer (B) thus obtainedpreferably has an average particle diameter of 100 nm or more, and morepreferably an average particle diameter of 100 to 300 nm.

<Cationic Surface Sizing Agent>

The cationic surface sizing agent of the present invention is obtainedby undergoing the first step to the third step. The cationic surfacesizing agent thus obtained has excellent dispersion stability withoutbeing affected by environments, especially, hardness or a pH of water,at the time of applying the surface sizing agent to the paper or paperboard. Hence, the cationic surface sizing agent can be uniformly appliedonto the surface of paper without being agglomerated. Accordingly, thecationic surface sizing agent of the present invention can impart anexcellent sizing property to paper or a paper board.

The cationic surface sizing agent of the present invention may be usedsingly, or may be used in combination with a water-solublehigh-molecular compound in the case of coating the surface of the paperor paper board. In the case of combination use, the water-solublehigh-molecular compound and the cationic surface sizing agent of thepresent invention are preferably mixed in proportions of 500:1 to 1:1,more preferably 100:1 to 5:1 by weight. Examples of the water-solublehigh-molecular compound include starches such as starch, enzyme-modifiedstarch, thermochemically modified starch, oxidized starch, esterifiedstarch, etherified starch (e.g., hydroxyethylated starch, etc.),cationated starch and the like; polyvinyl alcohols such as polyvinylalcohol, completely saponified polyvinyl alcohol, partially saponifiedpolyvinyl alcohol, carboxyl-modified polyvinyl alcohol, silanol-modifiedpolyvinyl alcohol, cation-modified polyvinyl alcohol, terminalalkyl-modified polyvinyl alcohol and the like; polyacrylamides such aspolyacrylamide, cationic polyacrylamide, anionic polyacrylamide,amphoteric polyacrylamide and the like; and cellulose derivatives suchas carboxymethylcellulose, hydroxyethyl cellulose, methyl cellulose andthe like.

The paper or paper board to be coated with the cationic surface sizingagent of the present invention is not particularly limited, and anypaper or paperboard can be coated with the cationic surface sizing agentof the present invention. Preferably, the surface of paper or a paperboard not containing an internal sizing agent, a neutralized paperhaving a Stockigt sizing degree of 2 second or less and a pH of papersurface of 6.5 to 8.5, or a neutralized paper board having waterabsorbency by a two minutes Cobb test of 100 g/m² or more and a pH ofpaper surface of 6.5 to 8.5 is coated with the cationic surface sizingagent of the present invention.

Since the cationic surface sizing agent of the present invention can beapplied without being affected by hardness or a pH of water, thecationic surface sizing agent is very useful. Moreover, the paper andpaper board coated with the cationic surface sizing agent of the presentinvention has an excellent sizing property and are used in variousfields.

EXAMPLES

Hereinafter, the present invention will be described specificallyreferring to examples and comparative examples, but the presentinvention is not limited to these examples.

Abbreviations illustrated in Example, Comparative Example and Tablerepresent the following compounds.

DM: Dimethylaminoethyl methacrylateDMAPAA: Dimethylaminopropyl acrylamide

St: Styrene

2EHA: 2-ethylhexyl acrylate2EHMA: 2-ethylhexyl methacrylateMMA: Methyl methacrylateLMA: Lauryl methacrylatenBA: n-butyl acrylatenBMA: n-butyl methacrylateiBA: i-butyl acrylateiBMA: i-butyl methacrylatetBMA: t-butyl methacrylateCHMA: Cyclohexyl methacrylate2HEA: 2-hydroxyethyl acrylate

Synthesis of Copolymer (A) Synthesis Example A1

Into a four-necked flask, dimethylaminoethyl methacrylate (DM) (20 partsby weight), 2-ethylhexyl acrylate (2EHA) (20 parts by weight), styrene(St) (60 parts by weight), n-dodecyl mercaptan (0.7 parts by weight) asa chain transfer agent, and toluene (32 parts by weight) as a solventwere charged, and the resulting mixture was stirred. Then, the mixturewas heated to about 105° C., and t-butyl peroxy isopropyl monocarbonate(1 part by weight) was added as an initiator, and the resulting mixturewas reacted at about 110° C. for 3 hours. Next, 90% by weight aceticacid (8.5 parts by weight) and water (300 parts by weight) were chargedinto the four-necked flask in order to neutralize a tertiary amino groupmoiety of the resulting copolymer and traces of remaining DM. Then,toluene was distilled away by heating distillation, and then contentswere diluted with water so that a solid concentration was 25% by weightto obtain a copolymer (A1).

Synthesis Example A2

Into a four-necked flask, dimethylaminoethyl methacrylate (DM) (30 partsby weight), n-butyl methacrylate (nBMA) (30 parts by weight), styrene(St) (40 parts by weight), t-dodecyl mercaptan (0.5 parts by weight) asa chain transfer agent, and isopropyl alcohol (32 parts by weight) as asolvent were charged, and the resulting mixture was stirred. Then, themixture was heated to about 85° C., and 2,2′-azobisisobutyronitrile (1part by weight) was added as an initiator, and the resulting mixture wasreacted at about 90° C. for 3 hours. Then, 90% by weight acetic acid(12.7 parts by weight) and water (300 parts by weight) were charged intothe four-necked flask in order to neutralize a tertiary amino groupmoiety of the resulting copolymer and traces of remaining DM. Next,isopropyl alcohol was distilled away by heating distillation, and thencontents were diluted with water so that a solid concentration was 25%by weight to obtain a copolymer (A2).

Synthesis Examples A3 to A8

Copolymers (A3) to (A8) were obtained by following the same procedure asin Synthesis Example A2 except for using the components illustrated inTable 1 in the proportions illustrated in Table 1, respectively. Inaddition, “DM neutralization percentage” described in the followingtable illustrates how much the tertiary amino group moiety of theobtained copolymer and the traces of remaining DM are neutralized. Forexample, when the DM neutralization percentage is 100 mol %, it meansthat these are completely neutralized.

Synthesis Example A9

Into a four-necked flask, dimethylaminoethyl methacrylate (DM) (20 partsby weight), styrene (St) (80 parts by weight), n-dodecyl mercaptan (1.5parts by weight) as a chain transfer agent, and isopropyl alcohol (32parts by weight) as a solvent were charged, and the resulting mixturewas stirred. Then, the mixture was heated to about 85° C., and2,2′-azobisisobutyronitrile (1.5 parts by weight) was added as aninitiator, and the resulting mixture was reacted at about 90° C. for 3hours. Next, 90% by weight acetic acid (8.5 parts by weight) and water(300 parts by weight) were charged into the four-necked flask in orderto neutralize a tertiary amino group moiety of the resulting copolymerand traces of remaining DM. Next, isopropyl alcohol was distilled awayby heating distillation, and then contents were diluted with water sothat a solid concentration was 25% by weight to obtain a copolymer (A9).

Synthesis Examples A10 to A18

Copolymers (A10) to (A18) were obtained by following the same procedureas in Synthesis Example A9 except for using the components illustratedin Table 1 in the proportions illustrated in Table 1, respectively.

TABLE 1 DM neutralization Component a Component c percentage Average(parts by Component b (parts by (90% acetic acid particle Copolymerweight) (parts by weight) weight) (parts by weight) diameter (A)Synthesis DM 2EHA St 100 mol % 30 nm or less A1 Example (20) (20) (60) (8.5) A1 Synthesis DM nBMA St 100 mol % 30 nm or less A2 Example (30)(30) (40) (12.7) A2 Synthesis DM tBMA St 100 mol % 30 nm or less A3Example (40) (40) (20) (17.0) A3 Synthesis DM nBMA St 100 mol % 30 nm orless A4 Example (20) (40) (40)  (8.5) A4 Synthesis DMAPAA iBMA 2EHMA St100 mol % 30 nm or less A5 Example (25) (30) (20) (25) (10.6) A5Synthesis DMAPAA nBMA 2EHA — 100 mol % 30 nm or less A6 Example (40)(50) (10) (17.0) A6 Synthesis DM nBMA — 200 mol % 30 nm or less A7Example (18) (82)  (7.6) A7 Synthesis DM tBMA St 100 mol % 30 nm or lessA8 Example (43) (20) (37) (18.3) A8 Synthesis DM — St 100 mol % 110 nm A9 Example (20) (80)  (8.5) A9 Synthesis DM — St 100 mol % 75 nm A10Example (25) (75) (10.6) A10 Synthesis DM 2HEA nBMA St 100 mol % 48 nmA11 Example   (12.5)   (17.5) (10) (60)  (5.3) A11 Synthesis DM tBMA2EHMA St 200 mol % 30 nm or less A12 Example (50) (15) (15) (20) (21.2)A12 Synthesis DM nBMA St 100 mol % 36 nm A13 Example (20) (40) (40) (8.5) A13 Synthesis DM nBMA — 100 mol % 30 nm or less A14 Example (30)(70) (12.7) A14 Synthesis DM tBMA 2EHMA St 100 mol % 30 nm or less A15Example (30) (30) (20) (20) (12.7) A15 Synthesis DM nBMA 2EHMA — 80 mol% 30 nm or less A16 Example (40) (40) (20) (13.6) A16 Synthesis DM nBMASt 100 mol % 30 nm or less A17 Example (18) (52) (30)  (7.6) A17Synthesis DM iBMA St 100 mol % 30 nm or less A18 Example (30) (30) (40)(12.7) A18 *1: Copolymers (A9) to (A12) are copolymers except thecopolymer (A) which is used in the present invention.

Synthesis of Cationic Surface Sizing Agent Example 1

An aqueous solution of the copolymer (A1) obtained in Synthesis ExampleA1 (400 parts by weight) (solid concentration 25% by weight), water (25parts by weight), and 90% by weight acetic acid (7.9 parts by weight)were charged into a four-necked flask and heated to about 85° C. Then,an aqueous solution of ferrous sulfate (2.2 parts by weight)(concentration 1% by weight) and an aqueous solution of ascorbic acid(1.8 parts by weight) (concentration 1% by weight) were added, andmethyl methacrylate (MMA) (11 parts by weight), n-butyl methacrylate(nBMA) (6 parts by weight), 2-ethylhexyl acrylate (2EHA) (6 parts byweight), styrene (St) (20 parts by weight) as hydrophobic monomers, andhydrogen peroxide solution (16 parts by weight) (concentration 8% byweight) were charged into a four-necked flask, and the resulting mixturewas reacted at about 85° C. for 3 hours. After the reaction,epichlorohydrin (7.1 parts by weight) was added to contents of thefour-necked flask, and the resulting mixture was reacted at about 85° C.for 3 hours and diluted with water so that a solid concentration was 30%by weight to obtain a sizing agent.

Example 2

An aqueous solution of the copolymer (A2) obtained in Synthesis ExampleA2 (400 parts by weight) (solid concentration 25% by weight) and water(150 parts by weight) were charged into a four-necked flask and heatedto about 85° C. Then, an aqueous solution of ferrous sulfate (5.2 partsby weight) (concentration 1% by weight) was added, and n-butylmethacrylate (nBMA) (36 parts by weight), n-butyl acrylate (nBA) (32parts by weight) and styrene (St) (32 parts by weight) as hydrophobicmonomers, and hydrogen peroxide solution (concentration 8% by weight)(38 parts by weight) were charged into a four-necked flask, and theresulting mixture was reacted at about 85° C. for 3 hours. After thereaction, epichlorohydrin (21.4 parts by weight) was added to contentsof the four-necked flask, and the resulting mixture was reacted at about85° C. for 3 hours, and diluted with water so that a solid concentrationwas 30% by weight to obtain a sizing agent.

Examples 3 to 8

Sizing agents were obtained by following the same procedure as inExample 1 except for using the components illustrated in Table 2 in theproportions illustrated in Table 2, respectively. In addition, thepolymerization initiators illustrated the following table are asfollows.

I1: Hydrogen peroxide solution (concentration 8% by weight)I2: Aqueous solution of ferrous sulfate (concentration 1% by weight)I3: Aqueous solution of ascorbic acid (concentration 1% by weight)I4: 2,2′-azobis(2-methylpropiondiamine)dihydrochloride

TABLE 2 DM neutralization Copolymer Water percentage Surfactant (partsby (parts by 90% acetic acid (parts by Component d weight) weight)(parts by weight) weight) (parts by weight) Example 1 A1 25 100 mol % —MMA nBMA 2EHA St (400) (7.9) (11)  (6)  (6) (20) Example 2 A2 150 — —nBMA nBA — St (400) (36) (32) (32) Example 3 A3 400 — — iBMA CHMA LMA —(400) (67) (100)  (67) Example 4 A4 50  50 mol % — tBMA 2EHA nBA St(400) (7.9) (22) (14) (12) (6) Example 5 A5 100 — — MMA iBMA LMA St(400) (20) (20) (20) (21) Example 6 A6 200 — — iBA LMA — St (400) (31)(31) (60) Example 7 A7 150 — — nBMA tBMA 2EHMA St (400) (28)  (8) (16)(48) Example 8 A8 400 — — iBA St (400) (133) (100)  QuaternizationAmount of Amount of Polymerization percentage copolymer (A) in componenta in Average initiator ECH(*1) copolymer (B) copolymer (B) particle(parts by weight) (parts by weight) (% by weight) (% by weight) diameterExample 1 I1 I2 I3 60 mol % 70 14 120 nm (16) (2.2) (1.8)  (7.1) Example2 I1 I2 — 120 mol %  50 15 170 nm (38) (5.2) (21.4) Example 3 I1 I2 — 90mol % 30 12 210 nm (88) (12.2)  (21.4) Example 4 I1 I2 I3 50 mol % 65 13110 nm (20) (2.8) (2.2)  (5.9) Example 5 I1 I2 — 80 mol % 55 13.75 180nm (31) (4.3) (11.9) Example 6 I1 I2 — 150 mol %  45 18 160 nm (46)(6.4) (35.6) Example 7 I1 I2 — 70 mol % 50 9 150 nm (38) (5.2)  (7.5)Example 8 I1 I2 I3 100 mol %  30 12.9 200 nm (88) (12.2)  (9.7) (25.5)(*1)ECH indicates epichlorohydrin.

Comparative Example 1

An aqueous solution of the copolymer (A9) obtained in Synthesis ExampleA9 (400 parts by weight) (solid concentration 25% by weight), water (300parts by weight), and 90% by weight acetic acid (7.9 parts by weight)were charged into a four-necked flask and heated to about 85° C. Then,epichlorohydrin (7.1 parts by weight) was added to contents of thefour-necked flask, and the resulting mixture was reacted at about 85° C.for 3 hours. Next, an aqueous solution of ferrous sulfate (7.9 parts byweight) (concentration 1% by weight) and an aqueous solution of ascorbicacid (6.2 parts by weight) (concentration 1% by weight) were added, andmethyl methacrylate (MMA) (40 parts by weight) as a hydrophobic monomer,n-butyl methacrylate (nBMA) (70 parts by weight) and 2-ethylhexylmethacrylate (2EHMA) (40 parts by weight) as hydrophobic monomers, andhydrogen peroxide solution (56 parts by weight) (concentration 8% byweight) were charged into a four-necked flask, and the resulting mixturewas reacted at about 85° C. for 3 hours. After the reaction, thereactant was cooled and diluted with water so that a solid concentrationwas 30% by weight to obtain a sizing agent.

Comparative Example 2

An aqueous solution of the copolymer (A10) obtained in Synthesis ExampleA10 (400 parts by weight) (solid concentration 25% by weight) and water(50 parts by weight) were charged into a four-necked flask and heated toabout 85° C. Then, an aqueous solution of ferrous sulfate (2.8 parts byweight) (concentration 1% by weight) was added, and methyl methacrylate(MMA) (18 parts by weight), n-butyl methacrylate (nBMA) (17 parts byweight) and n-butyl acrylate (nBA) (18 parts by weight) as hydrophobicmonomers, and hydrogen peroxide solution (20 parts by weight)(concentration 8% by weight) were charged into a four-necked flask, andthe resulting mixture was reacted at about 85° C. for 3 hours. After thereaction, epichlorohydrin (8.9 parts by weight) was added to contents ofthe four-necked flask, and the resulting mixture was reacted at about85° C. for 3 hours, and diluted with water so that a solid concentrationwas 30% by weight to obtain a sizing agent.

Comparative Examples 3 to 10

Sizing agents were obtained by following the same procedure as inComparative Example 2 except for using the components illustrated inTable 3 in the proportions illustrated in Table 3, respectively.

TABLE 3 DM neutralization Copolymer Water percentage Surfactant (partsby (parts by 90% acetic acid (parts by Component d weight) weight)(parts by weight) weight) (parts by weight) Comparative A9 300 100 mol %— MMA nBMA 2EHMA — Example 1 (400) (7.9) (40) (70) (40) Comparative A1050 — — MMA nBMA nBA — Example 2 (400) (18) (17) (18) Comparative A11 50— — tBMA 2EHMA 2EHA St Example 3 (400) (17) (17) (17) (17) ComparativeA12 200 — — nBMA iBMA — St Example 4 (400) (51) (36) (36) ComparativeA13 50 — (*1) MMA iBMA 2EHMA St Example 5 (400) (1.5)  (6)  (6) (20)(22) Comparative A14 200 — (*2) nBMA 2EHMA — St Example 6 (400) (8.3)(60) (30) (60) Comparative A15 100 — (*3) tBMA 2EHA iBA St Example 7(400) (4.1) (29)  (9) (29) (15) Comparative A16 600 — — tBMA 2EHMA 2EHA— Example 8 (400) (200)  (48) (52) Comparative A17 — 150 mol % — iBMAnBA — St Example 9 (400) (7.2)  (8)  (5) (13) Comparative A18 300 — —2EHMA St Example (400) (90) (60) 10 Quaternization Amount of Amount ofpercentage copolymer (A) in component a in Average Polymerizationinitiator ECH(*4) copolymer (B) copolymer (B) particle (parts by weight)(parts by weight) (% by weight) (% by weight) diameter Comparative I1 I2I3   60 mol %⁽*⁵⁾ 40 8 170 nm Example 1 (56) (7.9) (6.2) (7.1)Comparative I1 I2 — 60 mol % 65 16.25 140 nm Example 2 (20) (2.8) (8.9)Comparative I1 I2 — 80 mol % 60 7.5 130 nm Example 3 (25) (3.5) (5.9)Comparative I1 I2 I3 50 mol % 45 22.5 150 nm Example 4 (46) (6.4) (5.1)(14.8)  Comparative I1 I2 120 mol %  65 13  70 nm Example 5 (20) (2.8)(14.3)  Comparative I4 90 mol % 40 12  80 nm Example 6 (1.5) (16.0) Comparative I4 100 mol %  55 16.5  90 nm Example 7 (0.8) (17.8) Comparative I1 I2 — 30 mol % 25 10 230 nm Example 8 (113)  (15.7)  (7.1)Comparative I1 I2 — 70 mol % 80 14.4  70 nm Example 9  (9) (1.3) (7.5)Comparative I1 I2 — — 40 12 150 nm Example (56) (7.9) 10 (*1):Stearyltrimethyl ammonium chloride (*2): Cetyltrimethyl ammoniumchloride (*3): Polyoxyethylene cetyl ether (*4)ECH indicatesepichlorohydrin. ⁽*⁵⁾Copolymer (A) is quaternized before being subjectedto the second step.

Comparative Example 11

Into a four-necked flask, dimethylaminoethyl methacrylate (DM) (25 partsby weight), 2-ethylhexyl methacrylate (2EHMA) (15 parts by weight),styrene (St) (60 parts by weight), n-dodecyl mercaptan (1.5 parts byweight) as a chain transfer agent, and isopropyl alcohol (32 parts byweight) as a solvent were charged, and the resulting mixture wasstirred. Then, the mixture was heated to about 85° C., and2,2′-azobisisobutyronitrile (1.5 parts by weight) was added as aninitiator, and the resulting mixture was reacted at about 90° C. for 3hours. Next, 90% by weight acetic acid (10.6 parts by weight) and water(300 parts by weight) were charged into the four-necked flask in orderto neutralize a tertiary amino group moiety of the resulting copolymerand traces of remaining DM. Then, isopropyl alcohol was distilled awayby heating distillation. After the distillation of isopropyl alcohol,epichlorohydrin (11.9 parts by weight) was added, and the resultingmixture was reacted at 85° C. for 3 hours. Then, the reactant was cooledand diluted with water so that a solid concentration was 25% by weightto obtain a sizing agent. A neutralization percentage of the tertiaryamino group moiety of the copolymer and the traces of remaining DM was100 mol %, and a quaternization percentage of the obtained sizing agent(copolymer) was 80 mol %, and an average particle diameter of the sizingagent was 30 nm or less.

A sizing property (Stockigt sizing degree and water absorbency by a twominutes Cobb test) and a foaming property of the sizing agents obtainedin Examples and Comparative Examples were evaluated according to thefollowing method. The results of evaluations are illustrated in Table 4.

<Stockigt Sizing Degree>

Each of the sizing agents obtained in examples and comparative examples,oxidized starch, and tap water having hardness of 60 ppm (in terms ofCaCO₃) were mixed so as to be 0.4% by weight, 5.0% by weight, and 94.6%by weight, respectively, to prepare a coating solution. Next, theobtained coating solution was applied onto both surfaces of aneutralized high-quality base paper (basis weight 70 g/m², Stockigtsizing degree 0 second, pH of paper surface 7.6) not having an internalsizing agent added in such a way that the amounts of the solutionabsorbed at both surfaces was 30 g/m². Then, the coating solution wasdried at 90° C. for 90 seconds using a rotary drum dryer (manufacturedby KUMAGAI RIKI KOGYO CO., LTD., KRK rotary dryer) to obtain a coatedpaper.

Aside from this, when each of the above-mentioned coating solutions wasprepared, synthesized hard water with hardness of 2000 ppm (in terms ofCaCO₃) was added so that the hardness of a coating solution becomes 500ppm to obtain a coating solution with high hardness. The coatingsolution with high hardness was applied to a neutralized high-qualitybase paper by the same procedure as in the above to obtain a coatedpaper.

The Stockigt sizing degree of each coated paper obtained was measuredaccording to JIS P 8122.

<Water Absorbency by Two Minutes Cobb Test>

Each of the sizing agents obtained in examples and comparative examples,and tap water having hardness of 60 ppm (in terms of CaCO₃) were mixedso as to be 0.2% by weight and 99.8% by weight, respectively, to preparea coating solution. Next, the obtained coating solution was applied ontoone surface of a base paper for a liner (basis weight 180 g/m², waterabsorbency by a two minutes Cobb test 210 g/m², pH of paper surface 7.2)having an internal sizing agent added in such a way that the amount ofthe solution absorbed at one surface was 15 g/m². Then, the coatingsolution was dried at 90° C. for 90 seconds using the above-mentionedrotary drum dryer to obtain a coated paper.

Aside from this, when each of the above-mentioned coating solutions wasprepared, synthesized hard water with hardness of 2000 ppm (in terms ofCaCO₃) was added so that the hardness of a coating solution becomes 500ppm to obtain a coating solution with high hardness. The coatingsolution with high hardness was applied to a neutralized high-qualitybase paper by the same procedure as in the above to obtain a coatedpaper.

The water absorbency by a two minutes Cobb test of each coated paperobtained was measured according to JIS P 8140.

<Foaming Property>

The coating solution and the coating solution with high hardness used inthe evaluation of the Stockigt sizing degree were put in a mixer fordomestic use (manufactured by Panasonic Corporation, a fiber mixer), andstirred for 3 minutes. A height of a foam was measured after a lapse ofthree minutes from a stop of stirring.

<Stability Test>

The coating solution using the tap water and the coating solution usingthe synthesized hard water, which were used for the above-mentionedevaluation of a foaming property, were separated by filtration with a200 mesh metal gauze after the test of a foaming property, and stabilitywas evaluated from the weight of a residue in filtration. The case wherethe amount of a residue is smaller shows that the amount of anagglomerated substance is smaller, and the sizing agent has excellentdispersion stability.

TABLE 4 Stockigt sizing degree Two minutes Cobb test Foaming propertyStability test (seconds) (g/m²) (mm) (g) Synthesized SynthesizedSynthesized Synthesized Tap water hard water Tap water hard water Tapwater hard water Tap water hard water Example 1 20 18 44 52 20 22 Lessthan Less than 0.01 0.01 Example 2 18 18 52 60 20 19 Less than Less than0.01 0.01 Example 3 18 20 58 62 19 20 Less than Less than 0.01 0.01Example 4 21 19 64 70 20 22 Less than Less than 0.01 0.01 Example 5 1917 52 55 20 20 Less than Less than 0.01 0.01 Example 6 20 20 50 58 18 18Less than Less than 0.01 0.01 Example 7 22 21 42 45 17 19 Less than Lessthan 0.01 0.01 Example 8 20 19 55 63 18 18 Less than Less than 0.01 0.01Comparative 5 5 182 204 20 22 0.17 0.30 Example 1 Comparative 7 3 168192 22 25 0.13 0.18 Example 2 Comparative 8 3 120 157 21 24 0.12 0.35Example 3 Comparative 10 11 130 142 27 32 0.02 0.04 Example 4Comparative 5 2 152 183 28 32 0.12 0.31 Example 5 Comparative 22 8 54152 32 37 0.08 0.13 Example 6 Comparative 20 11 60 138 29 35 0.10 0.11Example 7 Comparative 5 6 175 182 21 21 0.15 0.25 Example 8 Comparative18 10 63 127 28 35 0.05 0.09 Example 9 Comparative 6 3 143 162 29 370.17 0.38 Example 10 Comparative 20 5 65 182 22 35 0.20 0.36 Example 11Hardness of tap water is 60 ppm (in terms of CaCO₃).

As illustrated in Table 4, the paper coated with the cationic surfacesizing agent prepared by the production method of the present inventionis found to have an excellent sizing property which compares favorablywith the case using tap water even when using the synthesized hardwater, and to have low water absorbency by a two minutes Cobb test tohardly absorb water. Moreover, it is found that the cationic surfacesizing agent prepared by the production method of the present inventionexhibits a low foaming property in any of use of tap water and use ofsynthesized hard water, and the sizing agent is excellent in theworkability of coating. Further, it is found that the amount of aresidue in filtration is small even when any of tap water andsynthesized hard water is used, and stability (dispersion stability) inthe coating solution is excellent.

On the other hand, the paper coated with the cationic surface sizingagent prepared by the method other than the production method of thepresent invention is found to have relatively a low sizing degree.Further, it is found that even when this paper has a relatively goodsizing property (Comparative Examples 2 and 7), the sizing degree isreduced to about one-half in the case of using synthesized hard water.Further, it is found that this paper has relatively high waterabsorbency by a two minutes Cobb test and extremely tends to absorbwater particularly when synthesized hard water is used. Furthermore,this surface sizing agent is found to extremely tend to foam whensynthesized hard water is used. Further, it is found that the amount ofa residue in filtration is large in any of use of tap water and use ofsynthesized hard water, and stability (dispersion stability) in thecoating solution is low.

1. A method for producing a cationic surface sizing agent comprising afirst step of obtaining a copolymer (A) by solution-polymerizing amonomer mixture which comprises a monomer having a tertiary amino group(a) in the amount of 15 to 45% by weight, a (meth)acrylic acid ester (b)in the amount of 15 to 85% by weight, and styrenes (c) in the amount of0 to 70% by weight in the presence of a chain transfer agent, wherein anester moiety of the (meth)acrylic acid ester (b) is a chainlike alkylhaving 4 to 18 carbon atoms, a cyclic alkyl having 4 to 18 carbon atoms,or aryl having 6 to 18 carbon atoms; a second step of obtaining acopolymer (B) by polymerizing the copolymer (A) and a hydrophobicmonomer (d) in an oxidation-reduction system using a water-solublefree-radical initiator and a heavy metal salt in the absence of asurfactant, wherein the copolymer (A) is used at the proportion of 30 to70% by weight with respect to the entire components including thecopolymer (B), and the monomer having a tertiary amino group (a) is usedso as to be 8 to 20% by weight with respect to the entire componentsincluding the copolymer (B); and a third step of obtaining a quaternaryammonium salt of the copolymer (B) by quaternizing a tertiary aminogroup present in the copolymer (B).
 2. The method according to claim 1,wherein the water-soluble free-radical initiator is hydrogen peroxide,and the heavy metal salt is ferrous sulfate.
 3. The method according toclaim 1, wherein the tertiary amino group moiety present in thecopolymer (A) is completely neutralized by using acid to be brought intothe form of an aqueous solution in the first step.
 4. The methodaccording to claim 1, wherein the copolymer (A) has an average particlediameter of 50 nm or less.
 5. The method according to claim 1, whereinthe quaternary ammonium salt of the copolymer (B) has an averageparticle diameter of 100 nm or more.
 6. The method according to claim 1,wherein 50 mol % or more of the tertiary amino group present in thecopolymer (B) is quaternized.
 7. The method according to claim 1,wherein the quaternization is performed by using epichlorohydrin.
 8. Themethod according to claim 1, wherein the monomer having a tertiary aminogroup (a) is at least one selected from the group consisting ofdialkylaminoalkyl (meth)acrylate and dialkylaminoalkyl (meth)acrylamide.9. A cationic surface sizing agent produced by the method according toclaim
 1. 10. A method for surface treating paper or a paper board,comprising a step of coating the surface of the paper or paper boardwith the cationic surface sizing agent according to claim 9 or a mixtureof this sizing agent and a water-soluble high-molecular compound. 11.Paper or a paper board prepared by the method according to claim
 10. 12.The paper or paper board according to claim 11, wherein the paper orpaper board before coated with a cationic surface sizing agent is paperor a paper board not containing an internal sizing agent, a neutralizedpaper having a Stockigt sizing degree of 2 second or less and a pH ofpaper surface of 6.5 to 8.5, or a neutralized paper board having waterabsorbency by a two minutes Cobb test of 100 g/m² or more, and a pH ofpaper surface of 6.5 to 8.5.